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In this paper, the approach of using magnetic circuits in giant magneto-impedance (GMI) current sensors is introduced for the first time in order to reduce the impact of magnetic disturbances on the sensor response. The studied current sensor had a toroidal structure. The GMI sensitive element circled the conductor carrying the measured current. The way to use a magnetic circuit in this configuration was established, and the rules of design and implementation were defined and validated by the simulation and by the measurements. The theoretical idea was to place the sensitive element on the surface of a magnetic circuit. However, in practical conditions, both simulation and measurement have demonstrated that a magnetic circuit must be placed at each side of the sensitive element, if the idea is to prevent from the effect of the different types of magnetic disturbances. [ABSTRACT FROM AUTHOR]

This paper deals with practical issues and solutions related to the use of the giant magnetoimpedance (GMI) for electrical current measurement. It presents an overview of a full attempt of design and realization of an almost industrial GMI-based current sensor or clamp. The sensor combines dc and ac measurements with the same flexible sensitive element. This paper addresses several practical problems encountered in a real measurement environment. In this context, main attention was paid to the impact of the influence quantities that largely condition the implementation strategies and solutions of the sensor. For the intended industrial application, these influence quantities first include the operating temperature. Its impact on the intrinsic sensor response was investigated in an almost industrial temperature range. Second, bending stress on the sensitive element is another involved influence parameter in the toroidal and flexible structure of the sensor. The effect of this was also characterized. Finally, the third considered influence parameter is the effect of magnetic disturbances. These include the eccentricity of the conductor of interest and the impact of the surrounding magnetic fields such as the earth’s field or fields produced by other conductors in close proximity to the sensor. Different strategies of implementation and solutions, taking into account the impact of influence parameters, were proposed and compared. A sensor prototype was realized, and its first performances were given. [ABSTRACT FROM AUTHOR]

The “magnetic differentiation” technique is an original method for magnetic-field measurement. It is used for giant magnetoimpedance (GMI) sensors. The response is very different from the classical impedance measurement. To measure the external field \textH\mathrm {ext} , small increments of magnetic field, alternatively positive and negative \pm \Delta H , are added to H_{\mathrm {ext}} by a small coil around the GMI wire. The measured signal is the slope of the curve of the impedance Z(H_{\mathrm {ext}})$ . The “magnetic differentiation” technique exhibits many advantages. The obtained response is a relatively simple curve with an odd symmetry. The zero of the sensor exactly corresponds to the zero magnetic field. The sensor is able to measure the “absolute zero” field, without any zero-adjustment. Around the zero-field point, the response is linear for a range of several tenths of A/m, with a very high sensitivity. The sensor response around the zero stays constant when the GMI wire is submitted to variable influence parameters, such as temperature or strain. Moreover, the measurement of high magnetic field can be easily made with an additional coil supplied by a closed-loop system; the operation point remains around the zero-field. Globally, the magnetic differentiation technique is an original way of using the GMI effect. The null signal at zero magnetic field, the linearity around the zero, and the odd response are very interesting properties, allowing the development of a new generation of GMI sensors. [ABSTRACT FROM AUTHOR]

Electrical current measurement by a giant magnetoimpedance (GMI) sensor may require the sensitive element (amorphous wire) to be aligned with the magnetic field produced by the conductor (toroidal configuration), which involves a bending stress. In this paper, a first study is made to investigate the impact of bending stress on a GMI sensor. For practical GMI sensor implementation, the offset and intrinsic sensitivity are crucial parameters. This is why these quantities have been evaluated in both diagonal and off-diagonal configurations. A Co-rich amorphous wire (from Unitika Ltd.) of 100~\mu \textm diameter and 15 cm length was used. The off-diagonal voltage was measured through a pick-up coil. The wire was bent over a cylinder with a radius of 2.5 cm. The excitation frequency was 800 kHz. In the diagonal configuration, the sensitivity at a given bias field \textHbias was decreased by 50% in the bent position compared to the straight position. The offset also decreased by 25%. In the off-diagonal configuration, the sensitivity around zero decreased by about 28%. The offset stayed quasi-null during the test. These results showed that the off-diagonal configuration seems to be best suited for an application as a current sensor that involves bending. The reversibility and repeatability of the bending effect have been evaluated under ten successive bending stresses. It was shown that the effect is quite reversible and repetitive. [ABSTRACT FROM AUTHOR]

In this paper, we propose a general model to evaluate the equivalent magnetic noise for an off-diagonal giant magneto-impedance (GMI) sensor utilizing a software-defined radio (SDR) as a digital receiver. Based on this SDR approach, an analog-to-digital conversion (ADC) of the voltage induced by the sensing element is directly performed. The signal processing is digitally achieved in real time. It includes a digital quadrature demodulation, a decimation, and a filtering. The approach allows to give the key rules for quantifying the white noise level of this digital implementation. The voltage noise spectral density of the ADC and of each SDR stage is given. The white noise level expected by the modeling was in good agreement with the measurements. With a sensing element composed of a 400 turn coil wound around a co-rich GMI wire, equivalent magnetic noise levels of 220 and 4.2 pT/ \sqrt Hz were obtained at 1 Hz and in the white noise region, respectively. The potential improvement of these performances, allowed by this digital conditioning, as well as limitations is also discussed. [ABSTRACT FROM PUBLISHER]

A proof-of-concept of the use of a giant-magneto-impedance (GMI) sensor for the realization of signal transmission under high isolation voltage is presented. This technology, which has never been used for gate driver units before, can potentially provide low coupling capacitance (<1 pF) and high insulation voltage capability up to 40 kV for a gap of 1 mm. The signal information is carried by a magnetic field emitted by a specially designed magnetic coil. The receiver acquires datum thanks to a dedicated high sensitivity and large bandwidth GMI sensor. The technique ensures a high galvanic isolation and provides potentially fast transmission rates while maintaining a low coupling capacitance between the transmitter and the receiver. The aim of this new technology would be to proceed well beyond the performances of coil–coil transmitters. This letter deals with the principles of implementation of this new technique. A prototype has been designed, developed, and tested. First results are given with a discussion about the potential performance and strategies of improvements. [ABSTRACT FROM AUTHOR]

Temperature dependence of giant magnetoimpedance (GMI) amorphous wires has been investigated in a quasi-industrial temperature range of [−20 °C; 120 °C]. Co-rich amorphous microwires, from Unitika Ltd, of $100~\mu $ m diameter and about 50 mm length were placed inside a regulated temperature chamber. The impedance modulus, as a function of the magnetic field, was measured using an impedance analyzer. The excitation current of the GMI wire was about 3 mA of amplitude and 1 MHz of frequency. In addition to the GMI ratio, particular attention was paid to the behavior of the intrinsic sensitivity and the offset, which are the most relevant quantities in a real GMI sensor implementation. The experimental results have showed that the impedance curve was changed with the temperature. The maximum sensitivity and the GMI ratio increased with temperatures ranging from −20 to 80 °C. Then, beyond 80 °C, the trend seemed to be reversed. Over the considered temperature range, and at typical bias field of H = 35 A/m, the intrinsic sensitivity varied with a temperature coefficient of 0.4%/°C, while the temperature coefficient of the offset was about 200 nT/K. [ABSTRACT FROM PUBLISHER]

The implementation and the performance of a software-defined radio (SDR) detector for the signal demodulation and processing in off-diagonal GMI sensors are presented. One of the underlying ideas of this SDR is to benefit from the possibility to obtain almost linear and asymmetric characteristics of the off-diagonal component around the zero field. Unlike the commonly used peak detectors, the implemented SDR detector allows retaining this feature, without using any bias field and additional techniques of offset canceling. The key rules for a successful implementation of the SDR detector are given in some details and its potential is addressed. The first performances of the sensor are given and discussed. These include response, sensitivity, and noise as well as dynamic range, linearity, and slew rate. [ABSTRACT FROM PUBLISHER]

A new high frequency and fully digital electronics was implemented for the conditioning of giant magnetoimpedance (GMI) sensors. The electronics are based on the use of a direct digital synthesizer as a high frequency source for the excitation of the sensing element and a software defined radio (SDR) that performs a direct analog-to-digital conversion, with over-sampling, and quadrature digital down conversion (DDC) of GMI voltage. This DDC includes digital mixers and digital decimation filters that ensure a low-pass filtering and a processing gain. The DDC outputs the in-phase and quadrature baseband digital signals. Except for an optional preamplifier and a voltage-to-current converter, the whole system is digital and fully programmable in real time using a high performance digital signal processor. The architecture of the developed electronics is given and the various aspects of the design are addressed. The performance and potential of the SDR are discussed throughout this paper. The dynamic range for the digital full scale output was between 95 and 120 dB. The out-of-band noise rejection was beyond our measurement instruments. The concept has been successfully applied and used for a GMI sensor and the first measurements were conducted. [ABSTRACT FROM AUTHOR]

In a giant magnetoimpedance (GMI) magnetic sensor, the magnetic field is measured by the voltage amplitude across the sensing element, the GMI wire. Most often, the amplitude of the high-frequency signal is measured by a peak detector, i.e., a diode—capacitor system. A new measurement technique has been developed, by measuring the root mean square (rms) value of the signal. For any signal, the rms value can be used to obtain information on the signal amplitude. In the frequency domain, this type of measurement is mainly well-suited and dedicated for the high-accuracy measurement of static or low frequency magnetic field. In the amplitude domain, rms-to-dc converters can be used for relatively low-amplitude signals, up to 1 V. The rms-to-dc converter has been used with a GMI sensor. Operation in open and closed loop has been tested. The closed loop allows obtaining a very good linearity, and a better bandwidth. Alternative magnetic field at 240 Hz can be measured. [ABSTRACT FROM AUTHOR]

Modeling and computing of mutual inductance between solid conductors or coils of rectangular cross section carrying uniform current and parallelepiped magnets of rigid polarization have been made. For this purpose, the integral approach using a quasi-static Green’s functions is used. The inductance is calculated between the total volume of a conductor and the equivalent current surfaces densities described by the Amperian model of permanent magnets. The analytical results are obtained after five integrations. It is to be noted that the formulas developed in this paper are more general that the ones established in the literature and can be used for optimization purposes. In addition, this paper is carried out without using any simplifying assumptions. Consequently, these expressions are accurate whatever the magnet dimensions are. This analytical formulation compared with finite element method one is suitable for the design of unconventional magnetic couplings, magnetically planar actuator, electric machines, wigglers, and so on. [ABSTRACT FROM AUTHOR]

A new analytical computation of magnetic flux distribution and eddy currents is proposed in this paper. Equations are set down for a plate subjected to a time-varying flux excitation. This method consists of using Neumann's boundary conditions in the flux-density diffusion equation to consider the instantaneous variations of the imposed flux waveform. The diffusion equation is solved by separation of variables and Duhamel's theorem. Different cases of imposed magnetic flux are studied: sinusoidal flux, flux ramp, and arbitrary time-varying flux. This new analytical method is a complement of the classical approach (with Dirichlet's boundary conditions) where induction at boundary needs to be corrected to fit the instantaneous total flux. In this paper, a distinctive method allows to compute the instantaneous distributions and corresponding losses directly from the experimental flux measurements on electromagnetic devices. The analytical expressions of magnetic flux density and eddy current distributions are explicitly given. The comparison between analytical and finite-element simulation results shows the validity of the new analytical method. [ABSTRACT FROM PUBLISHER]

An analytical method for the calculation of the magnetostatic scalar potential and the magnetic field created by a polyhedron-shaped permanent magnet is presented in this paper. The magnet is supposed to be uniformly magnetized. The magnetization is equivalent to distributions of magnetic charges: it is the coulombian approach. The analytical calculation is made by a surface integration on all the polygons that composes the polyhedron. For each polygonal surface, we have shown that it can be decomposed in a series of right triangles. An analytical solution in the particular case of the right triangle has been developed. By this way, the magnetostatic potential and the magnetic field of any polyhedral-shaped magnet can be analytically calculated. [ABSTRACT FROM AUTHOR]

The interaction force and torque between two parallelepiped magnets can be analytically calculated by “magnetic nodes.” The obtained expressions only depend on the corner positions. It leads F. Bancel to propose the notion of magnetic nodes situated at the corner positions. The force and torque components can be directly calculated with the magnetic nodes representation. The only hypothesis is that the magnets are supposed to be perfect (polarizations J and \J^\prime constant, rigid and uniform). The analytical calculation is made by replacing polarizations by distributions of magnetic charges on the poles. The torque is calculated for rotational movement of the second magnet around its center. The three components of the force and the torque can be written with functions based on logarithm and arc-tangent. The representation by magnetic nodes is correct from a mathematical point of view. But attention must be paid to the fact that the magnetic nodes cannot be isolated from the others. The whole force is correct even when the value on the magnetic nodes is not. Meanwhile, the magnetic node representation is very suitable for global interaction understanding and for force and torque calculation. [ABSTRACT FROM PUBLISHER]

Most of the systems working by magnet interactions can be calculated by superposition of the interactions between parallelepiped elementary magnets. Each elementary magnet is submitted to a force and a torque. By 3-D fully analytical calculation, up to now, only the force components problem has been solved. It was published for the first time in 1984. Until now, the torque components have never been analytically calculated because of the angular derivation. We have solved it, so that now all the interactions (energy, three forces components, and three torque components) can be expressed by analytical formulations. The only hypothesis is that the magnetizations J and J' are supposed to be rigid and uniform in each magnet. The analytical calculation is made by replacing magnetizations by distributions of magnetic charges on the magnet poles. The torque is calculated for rotational movement of the second magnet around its center. The three components of the torque are written with functions based on logarithm and arc-tangent. The results have been verified and validated by comparison with finite-element calculation. Analytical calculation owns many advantages in comparison with other calculation methods. The 3-D analytical expressions are difficult to obtain, but the expressions of energy, force, and torque are very simple to use. For example, the analytical expression can be included in optimization software allowing to directly. obtaining the shape optimization by a fast way. [ABSTRACT FROM AUTHOR]

High-resolution nuclear magnetic resonance (NMR) spectrometry is possible in nonhomogeneous magnetic fields—such as those in portable equipment—if the static and the radio-frequency (RF) magnetic fields are perpendicular and correlated in the measurement volume. From the easy-axis rotation theorem and the Amperian currents model, it is possible to exactly match two magnetic fields in two-dimensional systems. We derive a basic probe element that fulfills these conditions. Then we present a portable NMR probe design. The static and RF magnetic fields of the probe are matched on a large volume. [ABSTRACT FROM AUTHOR]